This invention relates to methods of preparing oxydiphthalic anhydrides, the oxydiphthalic anhydrides prepared thereby, and polyetherimides derived therefrom.
Oxydiphthalic anhydrides, such as 4,4′-oxydiphthalic anhydride, are important monomers for the preparation of polyetherimides having exceptionally high temperature performance and excellent solvent resistance. These properties are useful in high performance plastics applications such as advanced composites and electronic circuit materials.
The preparation of oxydiphthalic anhydrides typically proceeds by the reaction of halophthalic anhydrides with potassium carbonate. Reaction conditions include neat and solvent reactions and the presence of various catalysts. Conventionally, the catalyst is added to the mixture of the halophthalic anhydride and potassium carbonate. Reaction yields vary considerably with impurities in the halophthalic anhydride, for example 4 or 5 or 6 or 7-chlorophthalide (herein referred to simply as chlorophthalide), which can be present in amounts greater than 250 ppm.
It is of interest, therefore, to provide a method for oxydiphthalic anhydride preparation that affords high yields and a minimum of by-products even in the presence of impurities, and provide other improvements to the process, which are consistently and reproducibly applicable.